1. Field of the Invention
The present invention is directed to improvements in evaporative cooling systems, conditioning systems that utilize thermodynamic laws to cool a fluid. Namely, a change of a fluid from a liquid phase to a vapor phase can result in a reduction in temperature due to the heat of vaporization involved in the phase change.
2. Related Background Art
In a typical evaporative cooler, raw water is supplied to or recirculated through a heat exchanger and is vaporized by extracting heat from supply air flowing through the heat exchanger. Most readily available forms of raw water include various contaminants, most notably dissolved salts and minerals. In a recirculating evaporative cooling system, excess water supplied to the heat exchanger that has not evaporated is collected in a reservoir and then pumped back to the heat exchanger. As the water evaporates from heat exchange, minerals and salts dissolved in the raw water remain, building in concentration as the water volume decreases. Make-up water is supplied to the system to compensate for the evaporated water, but the salts and minerals remain and can become deposited on the heat exchanger as sealants if the concentration is too high.
In order to alleviate high concentrations of sealants, most evaporative cooling devices that use water incorporate a water bleed to drain to control salt and mineral content in the reservoir. The techniques to determine an effective amount of bleed are varied and well-known. In general, the amount of bleed is dependent on the level of mineral contamination in the feed water and water chemistry, but varies from as low as about 10% of the feed water for very fresh water to as much as 50% or more of the feed water where mineral content is high. Even where chemical treatment is utilized to extend solubility of the minerals, bleed is still required to replace water saturated with minerals with fresh water to prevent scaling within the evaporative process.
FIG. 3 represents a schematic of a typical direct evaporative cooler 100. Water or another suitable cooling liquid is recirculated from a reservoir 110 through a supply line 112 to a distributor 116 using a pump 114. Distributor 116 evenly distributes the supplied water over a heat exchanger, such as evaporative pad 118. Supply air 124 is passed through the pad, where it is cooled and humidified to exit as cooled air 126. The water fed from distributor 16 flows down and through the pad and evaporates as it meets the warm supply air 124. A bleed stream controlled by valve 120, for example, is removed from the system through bleed or drain line 121 to drain 122 to control mineral build-up in the water. Fresh make-up water is added as needed from water supply 128 to replace the water evaporated and bled. The make-up water can be controlled by a float valve or other level sensing device (not shown) provided in the reservoir 110.
FIG. 4 depicts a typical indirect evaporative cooler, in this instance a fluid cooler 200. Fluid cooler 200 includes a housing 202 having air inlets 204 and an air outlet 206. A sump 210 that functions as a reservoir is disposed at the bottom of housing 202. A heat exchanger 218, having a fluid inlet 218-1 and a fluid outlet 218-2, is disposed above sump 210. Water or another suitable coolant is drawn from sump 210 through supply line 212 using a pump 214. The pumped water is supplied to a spray head 216, which sprays the water over heat exchanger 218 so as to draw heat from the heat exchanger. The sprayed water is collected in the sump 210. As in the direct evaporative cooler, in order to control the concentration of salts and minerals in the cooling water, a bleed valve 220 is provided in supply line 212 in order to bleed off cooling water through bleed line 221 to drain 222. Air is drawn through air inlets 204 and out air outlet 206 using a fan 230 driven by a motor 232 via a belt. The fluid to be cooled is supplied to heat exchanger 218 through inlet 218-1 and discharged through outlet 218-2.
In operation, as shown in FIG. 4, cool air 226 is first passed over the outer surface of heat exchanger 218, through which flows a hot fluid to be cooled. The fluid to be cooled may be a liquid such as water, or a gas, such as air. The heat exchanger 218 is sprayed with a recirculated water stream using supply line 212, pump 214 and spray head 216 and an air stream is simultaneously generated to flow over the wet exchanger surface to evaporate water and produce cooling of the primary fluid inside the heat exchanger. As in the case in the direct evaporative system, a bleed or water from the recirculation sump is required to prevent mineral build-up. Make-up water is added from supply 228 to replenish the evaporated and bled water.
In both the direct and indirect evaporative cooling systems, the bled water is directed to drain and is otherwise not used. Such can result in substantial waste of cooling water. This waste can significantly increase the cost of operating the system and also place a significant burden on water supplies, particularly in areas where fresh water is scarce.